This invention relates to an apparatus for enriching oxygen in the combustion air of internal-combustion engines by means of a gas centrifuge.
Since increased oxygen content in the air can increase burnup rate and thereby increase power or reduce fuel consumption, there have for some time been efforts to operate internal-combustion engines with oxygen-enriched combustion air.
It is thus known from DE 195 43 884 C2 to enrich oxygen in the air by gas diffusion through a membrane. Since oxygen can be enriched sufficiently with such a membrane only at low engine speed, the known apparatus has a pressure tank providing compressed oxygen-enriched air for high speeds. The known apparatus thus involves considerable equipment expense.
DE 195 45 397 A1 also discloses an apparatus according to the preamble of claim 1. It proposes a multistage, electrically driven gas centrifuge which can enrich oxygen content to preferably 99%. However this print does not suggest how to achieve such oxygen enrichment economically.
In airplanes it is known to increase power temporarily by replacing combustion air by nitrous oxide, which has an oxygen content of 33% unlike air with an oxygen content of 21 vol % versus 78 vol % of nitrogen. In conventional motor vehicles, however, nitrous oxide cannot replace air if only for logistical reasons, but also because of the increased price and equipment expense.
The problem of the invention is therefore to provide combustion air having a sufficiently high degree of oxygen enrichment for an internal-combustion engine independently of speed economically without any great equipment expense.
According to the invention, the gas centrifuge for enriching oxygen in the combustion air is driven by an exhaust gas turbine. The kinetic energy of the exhaust gases which is otherwise lost is thus utilized for driving the gas centrifuge. The inventive apparatus thus permits economical operation.
The speed of the gas centrifuge enriching the oxygen content of the combustion air, and thus the increase in charging efficiency, i.e. in the oxygen-enriched air mass entering the cylinders, is thus linked with engine speed via the exhaust gas medium. This means that with rising engine speed and thus a rising flow rate of exhaust gas, the rotor speed of the gas centrifuge and thus the charging efficiency of oxygen-enriched combustion air to the cylinders rises.
It is favorable for realization of the inventive apparatus that exhaust gas turbines with high continuous speeds of 240000 rpm are available for turbocharging.
However, gas centrifuge speeds of e.g. 80000 revolutions per minute already suffice to achieve an oxygen enrichment of combustion air with an oxygen content of 33 vol % and more corresponding to nitrous oxide for example.
This will be illustrated by the following calculation based on a gas centrifuge having a rotor axially flowed through by combustion air in a cylinder interior.
At atmospheric pressure, i.e. on the rotor axis where no centrifugal force acts on the particles, particle number density no of a gas, i.e. the number of particles per unit of volume, is
no=xcfx81o/mxe2x80x83xe2x80x83(1)
where xcfx81 is the density of the gas at atmospheric pressure and m the mass of a molecule of the gas.
For nitrogen (N2) with xcfx81o=1.2505xc2x7kgxc2x7mxe2x88x923 and m=4.65175067xc2x710xe2x88x9226xc2x7k, particle number density no (N2) resulting on the rotor axis is thus                                           n            o                    ⁡                      (                          N              2                        )                          =                  1.2505          ·          kg          ·                                    m                              -                3                                      /            4.65175097                    ·                      10                          -              26                                ·          kg                                        =                              2.688235051            ·                          10              25                                ⁢                      xe2x80x83                    ⁢                      m                          -              3                                                              =                  1.000596565          ·                      N            L                              
where NL is the Loschmidt number with NL=2.68663xc2x72025xc2x7mxe2x88x923.
For oxygen O2 with xcfx81o=1.429 kgxc2x7m3 and m=5.31362901xc2x710xe2x88x9226 kg the particle number density resulting on the rotor axis is thus
no(O2)=1.000996982xc2x7NL.
With increasing radius r from the rotor axis the resulting particle number density for nitrogen n(N2) is
n(N2)=1.000596565xc2x7NLxc2x7exp{(6.7656339xc2x710xe2x88x928xc2x7kxc2x7(N2))xc2x7[n2]2xc2x7r2xc2x7mxe2x88x922}
while the particle number density for oxygen is
n(O2)=1.000996982xc2x7NLxc2x7exp{(7.7255698xc2x710xe2x88x928k(O2))xc2x7[n2]2xc2x7r2xc2x7mxe2x88x922}
where the exponential term in curly brackets results from the Maxwell-Boltzmann distribution law.
In accordance with the radius from the rotor axis of the gas centrifuge one thus obtains for nitrogen and oxygen in the air the particle number densities shown in the diagram according to FIG. 1. The divergent curves for oxygen (O2) and nitrogen (N2) in this diagram document successive increasing relative separation of oxygen and nitrogen molecules with increasing distance from the rotor axis at a rotor speed of 80000 revolutions per minute. That is, at this rotor speed and a radius of 7.5 centimeters of the rotor or the cylinder interior of the gas centrifuge, the particle number density of oxygen in the air increases from about 0.5xc2x71025 mxe2x88x923 on the rotor axis to about 2.7xc2x71025 mxe2x88x923, i.e. more than five times, but for nitrogen from about 2.0xc2x71025 mxe2x88x923 to about 8.7 1025 mxe2x88x923, i.e. only 4.4 times. That is, at a speed of 80000 revolutions per minute and a cylinder interior radius of 7.5 centimeters, the oxygen content on the cylinder interior wall is about 40 vol % versus 20 vol % in the air supplied to the gas centrifuge.
With the inventive apparatus one can thus readily obtain a power increase in the engine corresponding to that caused by supplying nitrous oxide.
While in engines operated with normal combustion air the share of incompletely burnt hydrocarbons rises at higher speed because there is not enough time for complete combustion, the inventive apparatus ensures with its enriched oxygen content in the combustion air that complete combustion takes place even at higher speeds, thereby clearly reducing the pollutant content, in particular the CO content, the content of soot particles and similar non- or only partly oxidized carbon compounds.
It is evident that even greater oxygen enrichment can be achieved at a further increase in speed of the rotor of the gas centrifuge and/or an increasing radius of the cylinder interior of the gas centrifuge, so that the content of nitrogen oxides in the exhaust gas can ultimately also be reduced over conventional engines, as well as ozone formation, which is attributed in particular to nitrogen oxides as the precursor substances.